Explanation: Evolutionary forces cause different genes to change at different rates. Those genes upon which evolutionary forces are acting strongly change more rapidly, while those upon which evolutionary forces are not acting strongly stay relatively the same.

____ involves changes in allele frequencies from one generation to the next.

Microevolution

Explanation: Microevolution refers to small-scale evolution. For example, if a trait in a parent generation is 60% A and 40% a, then microevolutionary changes may lead to 65% A and 35% a in the next generation.

Stabilizing Selection

Selection against the extremes of the phenotypic distribution.

Explanation: This type of selection is called stabilizing selection because it favors the average version of a trait, which decreases the genetic diversity for this trait in the population.

Directional Selection

Selection for one allele over the other alleles.

Explanation: This type of selection is called directional selection because it favors one extreme form of a trait, so the average form of the trait moves in that direction.

A ______ is a local population of organisms that have similar genes, interbreed, and produce offspring.

Deme

Explanation: Demes are interesting to geneticists because they can tell them how gene frequencies change among individuals that reproduce with one another. The term gene pool is not correct here because a gene pool is defined as all of the genetic information in a breeding population (not all of the organisms in a population). The gene pool is all of the genetic information that a deme has.

The population is in equilibrium.

The frequency of alleles does not change from one generation to the next.

Explanation: Populations that are in equilibrium are not evolving with respect to a specific allele.

The population is not in equilibrium.

The population is not in equilibrium.

Explanation: Populations that are not in equilibrium are evolving with respect to a specific allele.

Disruptive Selection

Selection for both extremes of the phenotypic distribution.

Explanation: This type of selection is called disruptive selection because the pattern of variation is discontinuous. Individuals at both extreme ends of the range produce more offspring than do the remainder of the population. Given enough time, this pattern can result in a speciation event as those in the middle fail to survive and reproduce and two new species arise at the extremes.

In regards to sickle-cell anemia, the ____ genotype is beneficial because it allows for resistance to malarial infection without risk of death.

AS

Explanation: The AS genotype means that an individual has one healthy allele (A) and one sickle-cell allele (S). Although two sickle-cell alleles would mean that a person has sickle-cell anemia and is at risk of death, one sickle-cell allele allows a person to be resistant to malarial infection while only having minor complications from the presence of the S allele.

Perhaps the best evidence ever documented of natural selection operating on a heritable trait concerns a type of moth, Biston betularia, found in England. Prior to the Industrial Revolution, these moths were ____.

white peppered with black

Coin tosses can demonstrate the effects of genetic drift. Imagine that heads and tails are two alleles in a population. Consider each coin toss to represent a member of the population. Which of the following statements describes the effect that you see here?

Smaller populations have a greater chance of having one allele expressed disproportionately.

Founder Population

It is a smaller population (usually less than a few hundred individuals) that has migrated out of the larger parent population.

Gene flow ____ the genetic variation between two populations.

decreases

Explanation: The biological traits that are expressed in two different populations become more similar when gene flow occurs, as the two populations interbreed and exchange genetic material. Some rare traits may die out.

____ is the only source of new genetic variation in a population.

Mutation

Huntington’s chorea is a genetic abnormality that causes degeneration of parts of the brain that control body movement and abilities such as speech production, triggering involuntary jerky movements of the arms and legs as well as dementia. A person needs only one allele from a parent to have the disease. Why has such a debilitating disease not been removed from the gene pool?

People pass the gene on before they know that they have the disease.

The following figure depicts the results of a study exploring how matrilocal and patrilocal social structures impact genetic diversity. The six different color bars each represent a different population for which mtDNA or Y-Chromosome DNA diversity was measured. Which of the following statements correctly describe how gene flow is at work?

1. The results support that the out-migration of females and the out-migration of males produce different patterns of genetic diversity.

2. Patrilocal societies exhibit less variation in Y chromosome DNA because males only reproduce with individuals within their social group.

3. Matrilocal societies exhibit more variation in Y chromosome DNA because females only reproduce with individuals within their social group.

Most mutations are due to random changes in the DNA (spontaneous), rather than due to exposure to toxic environmental circumstances (induced).

TRUE

EX: Most mutations have no known cause. They are simply DNA copying errors.

The following figure presents blood type frequencies (A, B, AB, O; MM, MN, NN) in three distinct populations (Dunkers, Germans, Americans). You are a scientist who is studying blood type frequencies and you are trying to determine in which population genetic drift has occurred. Correct the statement below by replacing the mistake with the word that will make it correct.

Genetic drift occurred in the ________.

Dunker

Which of the following are examples of hemoglobinopathies (blood diseases related to hemoglobin) that provide a strong selective advantage in areas where malaria is prevalent?

1. sickle-cell anemia

2. thalassemia

3. glucose-6-phosphate dehydrogenase (G6PD) deficiency

Point Mutation

Replacement of a single nitrogen base with another base, which may or may not affect the amino acid for which the triplet codes.

Frameshift Mutation

The change in a gene due to the insertion or deletion of one or more nitrogen bases, which causes the subsequent triplets to be rearranged and the codons to be read incorrectly during translation.

Transposable Element

Mobile pieces of DNA that can copy themselves into entirely new areas of the chromosomes.

Click on the cells where mutations have the greatest consequences for future generations.

Mutations that occur in the gametes have the greatest consequences for future generations. This is because gametes can transfer these mutations to their offspring. The human mutation rate is higher in male sex cells (sperm) than in female sex cells (eggs).

What does fitness measure?

The number of offspring that an individual has

A ____ is a local population of organisms that have similar genes, interbreed, and produce offspring.

deme

Genetic drift occurs more often in exogamous human groups.

False

In a small population, genetic drift operates over a ____.

relatively short period of time.

1. The melanic (black) phenotype had two possible genotypes.

2. The nonmelanic (white peppered with black) phenotype was only present in 10% of the population.

3. The melanic (black) phenotype had a higher frequency than the nonmelanic (white peppered with black) during the industrialization period.

Which of the following can lead to reproductive isolation?

1. a mountain range

2. a large body of water

3. separated landmasses

All human populations have the same genetic frequencies.

False

Which of the following must be true in order for a specific allele in a population to remain in a state of equilibrium?

1. No mutation, natural selection, or gene flow occur in relation to a specific allele.

2. The population is large.

3. Mating is random.

The principle used to determine whether an allele is experiencing evolution is called the ____ law of equilibrium.

Hardy-Weinberg

Populations that are geographically situated next to one another always experience gene flow.

False

Which of the following statements about the founder effect is/are correct?

1. A founder population is small, usually less than a few hundred members.

2. The genetic ratios in a founder population are not representative of the parent population.

3. A founder population's genetic ratios diverge from the parent population's after isolation.

The generation following the one in the illustration has offspring with genetic frequencies of 5% AA, 65% aa, and 30% Aa. Is the newer population in equilibrium or not in equilibrium with the original population?